Approximately 5% of the U.S. population have disfiguring birthmarks. Recently, lasers have been used to heat and destroy nevus flammeus, a common congenital hemangioma, most often called port wine stain (PWS). Not all PWS birthmarks respond to treatment with the commonly used argon-ion laser. Older patients and those with purple lesions respond better and with less risk than younger patients or those with pink lesions. Present laser treatment of PWS birthmarks may lead to scarring, destruction of the epidermis, infection, and loss of normal melanin pigmentation. A laser technique called "selective photothermolysis" has been advocated for the treatment of PWS birthmarks by a research group at Massachusetts General Hospital. With the proper choice of color and pulse duration of laser, targeted tissue can be irradiated specifically and heated to a narrowly defined temperature range to cause denaturation without vaporization of specific, tiny blood vessels causing PWS. Damage to surrounding tissue is avoided. Although target specificity of blood vessels has been demonstrated with this technique, the concept has not been applied clinically because no ideal laser has been available. A laser with the proper properties for selective photothermolysis can be developed by extending the pulse duration of a flashlamp excited dye laser. Research is required to develop this laser, but the problem areas have been defined and reasonable approaches to overcome the difficulties are available. The appropriate NIGMS program to monitor this research is the Physiology and Biomedical Engineering Program. Research on the mechanisms that limit dye laser pulse duration such as triplet quenching and thermal distortion is proposed. A novel laser resonator configuration has recently been devised that minimizes the effects of thermal distortion and should allow longer pulses. A research prototype laser will be assembled based on the findings of the research program and turned over to the Wellman Laser Laboratory of the Massachusetts General Hospital's Dermatology Department for evaluation. Their evaluation will comprise part of the final report for Phase I. If the evaluation is positive, a Phase II program to develop a therapeutic laser will be proposed. A market study by Boston College Graduate School of Management has shown that there may be as much as a $20 million market for lasers for treatment of PWS. The demand for a selective photothermolysis laser usable in the treatment of other ailments has not been studied but is expected to be many times greater than that for PWS.